The invention pertains to methods of implanting dopants into semiconductor structures, and in particular embodiments pertain to methods of forming CMOS constructions. The invention also pertains to semiconductor structures.
It is common for semiconductor structures to comprise p-channel devices adjacent n-channel devices. For instance, static random access memory (SRAM) and logic devices frequently comprise p-channel transistor devices adjacent n-channel transistor devices, or in other words frequently comprise PMOS devices adjacent NMOS devices. A construction comprising PMOS and NMOS devices can be referred to as a CMOS construction.
A prior art method for fabricating a CMOS construction is described with reference to FIGS. 1-4. Referring initially to FIG. 1, a fragment 10 of a semiconductor construction is illustrated. Fragment 10 comprises a substrate 12 having a dielectric material 14 and a semiconductive material 16 provided thereover. Substrate 12 can comprise, for example, monocrystalline silicon; dielectric material 14 can comprise, for example, silicon dioxide; and semiconductive material 16 can comprise, for example, either amorphous or polycrystalline silicon.
For purposes of the discussion that follows, the semiconductive material of substrate 12 can be referred to as a first semiconductive material, and the semiconductive material 16 can be referred to as a second semiconductive material. Additionally, fragment 10 can be referred to as a semiconductor structure. To aid in interpretation of the claims that follow, the terms xe2x80x9csemiconductive substratexe2x80x9d and xe2x80x9csemiconductor substratexe2x80x9d are defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term xe2x80x9csubstratexe2x80x9d refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.
A dashed line 18 subdivides fragment 10 into a pair of defined regions 20 and 22, with one of the regions ultimately being utilized for PMOS constructions and the other of the regions ultimately being utilized for NMOS constructions. Dashed line 18 can be considered an imaginary boundary segregating regions 20 and 22 from one another.
Referring to FIG. 2, semiconductor fragment 10 is illustrated in top view, wherein it is shown that semiconductive material 16 and dielectric material 14 are patterned into the shape of a line (dielectric material 14 is not visible in the view of FIG. 2), with such line extending across regions 20 and 22. It is noted that the line can extend entirely across regions 20 and 22, or can extend only partially across one or both of regions 20 and 22. Semiconductive material 16 can ultimately be utilized to form gates for transistor devices associated with regions 20 and 22.
Referring to FIG. 3, a photoresist mask 24 is shown formed over region 22, while leaving region 20 uncovered. Mask 24 can be formed by photolithographic processing methods. Specifically, mask 24 can be formed by initially providing a layer of photoresist across both regions 20 and 22, and subsequently exposing the photoresist to a patterned beam of radiation. The patterned beam of radiation selectively exposes the photoresist over one of regions 20 and 22 to the radiation, while leaving the photoresist over the other of regions 20 and 22 not exposed. A solvent can then be utilized to selectively remove the photoresist from over region 20, while leaving the photoresist over region 22. The photoresist utilized for forming mask 24 can be either positive photoresist or negative photoresist, and accordingly it can be either the portion over region 20 which is selectively exposed to radiation, or the portion over region 22 which is selectively exposed to radiation.
After patterned mask 24 is formed, fragment 10 is exposed to a first dopant implant. The dopant of the first implant is illustrated by downwardly extending arrows 26. The dopant can be either n-type or p-type conductivity-enhancing dopant, and can be implanted to be primarily within either substrate 12 or semiconductive material 16 of region 20. For instance, if region 20 is ultimately to comprise a PMOS device, dopant 26 can comprise n-type conductivity-enhancing dopant and can be implanted to form an n-type doped region 28 within substrate 12.
A second dopant 30 is implanted after the implant of first dopant 26, and is provided to be primarily in either semiconductive material substrate 12 or semiconductive material 16; and will be provided to be primarily in whichever of materials 12 and 16 did not primarily contain the implant of dopant 26. Accordingly, if dopant 26 was primarily directed into semiconductive substrate 12, dopant 30 will be primarily directed into semiconductive material 26 to form an implant 32 within material 26. If region 20 is ultimately to be utilized for forming a PMOS device, implant 32 can comprise p-type dopant.
It is to be understood that dopants 26 and 30 can both be implanted into both of semiconductive substrate 12 and semiconductive material 16; however, the dopants will typically be implanted to a heavier concentration in one of either the substrate 12 or material 16 than in the other of the substrate 12 and material 16. In the shown embodiment, first dopant 26 is implanted to a heavier concentration in semiconductive substrate 12 than in semiconductive material 16, and second dopant 30 is implanted to a heavier concentration in semiconductive material 16.
Mask 24 protects region 22 from receiving either of dopants 26 or 30 therein.
Referring to FIG. 4, patterned mask 24 (FIG. 3) is removed, and a second patterned mask 33 is formed. Mask 33 covers region 20, while leaving region 22 exposed. Mask 33 can be formed by processing similar to that described above with reference to mask 24.
After mask 33 is formed, a first dopant 34 is implanted into region 22. Dopant 34 can be either an n-type or p-type dopant, and can be provided primarily into either semiconductive substrate 12 or semiconductive material 16. If region 22 is ultimately to be utilized for forming an NMOS device, dopant 34 can comprise p-type dopant, and can be provided primarily into semiconductive substrate 12 to form a doped region 36.
After the implant of dopant 34, a second dopant 38 is implanted into region 22. Second dopant 38 is directed into whichever of semiconductive material 16 and semiconductive substrate 12 did not primarily receive the implant of first dopant 34. Accordingly, in the shown embodiment dopant 38 can be utilized to form an implant region 40 within semiconductive material 16. If region 22 is ultimately to be utilized for forming an NMOS device, dopant 38 can comprise an n-type dopant, and can accordingly be utilized to dope semiconductive material 16 of region 22 to n-type conductivity type.
A solid boundary replaces dashed line 18 within semiconductive material 16 and substrate 12 of FIGS. 3 and 4 to indicate that a border extends along the line 18 within materials 16 and 12. The border within material 16 delineates a boundary where dopant regions 32 and 40 meet; and the border within substrate 12 delineates a boundary where dopant regions 28 and 36 meet.
A problem which can occur during the prior art processing of FIGS. 1-4 is that dopant can migrate between doped regions 32 and 40 during subsequent thermal processing of fragment 10. For instance, if region 32 is a p-type doped region and region 40 is an n-type doped region, it is found that n-type dopant from region 40 can migrate into region 32 and change the electrical characteristics of semiconductive material 16 within region 20, and/or that p-type dopant from region 32 can migrate into region 40 and change the electrical characteristics of semiconductive material 16 within region 22. Such change in electrical characteristics can alter performance of electrical devices formed within regions 20 or 22, and even render such devices inoperable. It would be desirable to develop semiconductor fabrication technologies which alleviate or prevent dopant diffusion between regions 32 and 40 of semiconductive material 16.
In one aspect, the invention encompasses a method of implanting dopant into a semiconductor structure. A semiconductor structure is provided comprising a first semiconductive material and a second semiconductive material over the first semiconductive material. The structure further comprises a defined first region and a defined second region adjacent the first region. A photoresist mask is formed over the first region, and subsequently a first dopant is implanted into at least one of the first and second semiconductive materials of the second region. After the first dopant is implanted, a second dopant is implanted into at least one of the first and second semiconductive materials of the second region while at least some of the photoresist mask remains over the first region. The photoresist mask has a periphery at a first location of the semiconductor structure during the implanting of the first dopant, and such periphery is shifted to a second location prior to implanting of the second dopant.
In other aspects, the invention encompasses methods of formation of CMOS constructions; and in yet other aspects the invention encompasses semiconductor structures.